1. Field of the Invention
The present invention relates to improved wire bonds and bond pads of semiconductor devices. More specifically, the present invention relates to a wire bond structure that provides a stronger attachment to a bond pad without introducing excessive force to the substrate during attachment, a bond pad with self-locking characteristics, and methods for making the same.
2. Description of Related Art
Semiconductor devices comprising semiconductor chips and lead frames are well known. A semiconductor chip having one or more semiconductor elements is generally mounted on a mounting area of a lead frame, and each region of the element, such as a transistor, wire, or passive device, and the like, is connected with a lead of the lead frame by a thin bonding wire typically of gold or aluminum. For connection with the bonding wire, each region of the semiconductor is provided with an electrode. In an integrated circuit chip, regions are usually connected to each other by interconnection on the chip, and for connection with a lead outside, a special part of the interconnection called a bond pad or electrode is prepared. Generally, a bonding wire is connected to the electrode or bond pad by means of thermocompression or thermosonic bonding. Usually, to carry out the bonding, a small ball is formed at the end of the bonding wire, and then pressed onto the electrode under high temperature while the wire is excited ultrasonically.
Bonding depends upon various conditions—mechanical pressure, temperature, strength of the electrode or bond pad, power of the ultrasonic wave, and time, among other factors. One type of failure is produced by the ball at the end of the bonding wire, which, being mechanically hard brings about structural deformation and destruction of the substrate upon compression. A typical method for bonding a thin metal wire by ultrasonic thermocompression bonding is the so-called on-element bonding. In this method, a thin metal wire is ultrasonically thermocompression-bonded to an electrode formed adjacent to an impurity region that is formed to constitute a functional element. This method, however, has problems in that distortions or cracks are generally produced in the electrode or substrate. As is presently known in the art, low-k dielectric materials are easily damaged during wire bond operations. Insertion of a wire bond may cause excessive forces that could otherwise distort, stress, or crack the pad and underlying substrate material. Furthermore, the strength of the bond is jeopardized if micro cracks are introduced during the bonding process.
In U.S. Pat. No. 5,550,083 issued to Koide et al., issued on Mar. 29, 1994, entitled “PROCESS OF WIREBOND PAD REPAIR AND REUSE,” a wire bonding method is taught where wires are attached to pads, and subsequently disconnected for repair. A second pad is formed on the first pad, and a second wire is bonded to the second pad. The wire bond is attached by thermocompression, which can result in forces capable of causing distortion, stress, or cracks in the pad or underlying substrate.
In U.S. Patent Application Publication No. US2002/0177296 published on Nov. 28, 2002 by Ball, entitled “METHOD OF IMPROVING INTERCONNECT OF SEMICONDUCTOR DEVICES BY UTILIZING A FLATTENED BALL BOND,” a method of forming a semiconductor device assembly having a wire bond is taught where one portion of the connecting structure is flattened prior to attachment. The flattened portion is created with additional force and power applied during the formation of the wire bond.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a wire bond structure and method for making the same that can be formed without causing distortion, stress, or cracks in the pad or underlying substrate during formation.
It is another object of the present invention to provide a wire bond structure and method for making the same that provides for stronger bond retention without requiring excessive attachment force during formation.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.